The present invention relates to a locking mechanism for a rotation seat such as a driver seat.
As a rotating mechanism for a seat such as a driver seat there generally is known, for example, such a rotating mechanism as is disclosed in Japanese Utility Model Application Publication No. 5-18961. This type of seat rotating mechanism has a member fixed to an underside of the seat and a member (base member) fixed to a seat installed place (base). The member fixed to the underside of the seat is supported so as to be rotatable with respect to the base member. By such a configuration there is obtained a rotation seat which is rotatable with respect to the base.
In case of installing and using such a rotation seat in an industrial vehicle for example, the rotation seat, in an ordinary mode of use, is turned to the front side and fixed so that an operator sifting thereon can perform operations. For example, in backward movement of the vehicle, the rotation seat is rotated in a predetermined direction different from the front side and is fixed. Therefore, it is necessary to provide a locking mechanism for switching between an unlocked state in which the rotation seat can rotate and a locked state in which the rotation seat cannot rotate.
As a configuration of such a locking mechanism there is conceivable a configuration wherein a guide slot and a locking recess continuous from an intermediate portion of the guide slot are formed in a base member, and a stopper member guided by the guide slot and lockable to the locking recess is attached to a member secured to an underside of a seat, the stopper member being urged by a resilient member such as a coil spring in a direction (locking direction) in which it is locked to the locking recess. The locking recess has a tapered shape such that the width thereof becomes narrower with distance from the guide slot. Correspondingly to the width of the locking recess, the width of the stopper member also becomes narrower toward a front end thereof located on the locking recess side. The stopper member is supported by being fitted in a supporting slot formed in the member secured to the underside of the seat. Correspondingly to the stopper member, the width of the supporting slot also becomes narrower toward a front end thereof located on the locking recess side. In this locking mechanism, for unlocking the rotation seat, a lever connected to the stopper member is operated to move the stopper member in a direction (toward the guide slot) opposite to the above locking direction, while for locking the rotation seat, the operation of the lever is slackened, thereby causing the stopper member which has undergone an urging force from the resilient member to move in the locking direction into engagement in the locking recess.
In the above locking mechanism, when rotating the rotation seat in a different direction and locking it in this state, the stopper member operates in the following manner. First, the stopper member moves while being guided along the guide slot, thereafter, when the stopper member arrives at the position of the locking recess lying in an intermediate portion of the guide slot, the stopper member moves in the locking direction and is locked to the locking recess under the urging force of the resilient member, whereby the rotation seat is locked. Since the locking recess and the stopper member are tapered as described above, the stopper member is easy to enter the locking recess during movement of the stopper member along the guide slot.
In such a locking mechanism, when the rotating operation of the rotation seat is performed at low speed, the stopper member gets into the locking recess and is locked positively by the locking recess. However, when the rotating operation of the rotation seat is performed at high speed, even if the stopper member gets into the locking recess, there still remains a strong force in the moving direction (guiding direction) along the guide slot due to an inertia force of the rotation seat. At this time, since the stopper member and the locking recess are of such a shape as described above, the stopper member undergoes a force acting in a direction (toward the guide slot) leaving the locking recess opposite to the locking direction at both contact portions thereof with the locking recess and with the supporting slot. When this force exceeds the urging force of the resilient member, the stopper member returns to the guide slot without being locked by the locking recess. As a result, the stopper member passes the locking recess without being locked to the locking recess, thus giving rise to the problem that the rotation seat cannot be locked at the predetermined position.
The present invention is directed to a locking mechanism for a rotation seat wherein a stopper member is locked positively to a locking recess even when the rotation seat is rotated at relatively high speed.